Low-temperature refrigeration system



Jan. 1l, 1949. s. c. COLLINS 2,458,894

LOW TEMPERATURE REFRIGERATION SYSTEM Filed Oct. 14, 1940 2 Shees-Sheet l MCG-@w @Wim/maga.

Jan. 1l, 1949. s. c. coLLlNs 2,458,894

LOW TEMPERATURE REFRIGERATIQN SYSTEM Filed oct. 14, 1940 y '2 sheets-sheet 2 Compresa-0r 33M loyaal.,

Patented Jari. 11, i949 LOW-TEMPERATURE REFRIVGER'ATIO-N SYSTEM samuel c. collins, cambridge, Mass., assisnor, by mesne assignments, to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Application october 14, 1940, serial No. 361,137

(ci. erf-17's) 14: Claims.

The invention relates to a refrigeration system for the production of low temperatures and is particularly directed to a low temperature refrigeration system involving the expansion of compressed gases with the performance of external work to produce low temperatures and to novel elements of such a system whereby low temperatures of the order of the temperature of liquid air and/lower may be produced.

A principal object of the invention is the provision of a highly eicient refrigerationy system for the production of low temperatures' by the expansion of compressed gases with the performance of external work.

A further object of the invention is the provision of a low temperature refrigeration system involving the expansion of compressed gases with external work in which at least the low temperature portion of the system including the machine for expansion of the compressed gases is hermetically sealed. l

Other objects and advantages of the invention will appear from the following description of the invention.

The low temperature refrigeration system of the invention is based upon the production of low temperatures by the expansion of compressed gases with the performance of external work. In order to make available the lowest temperatures helium is preferably utilized asthe refrigerant medium, although the principles of the invention may be applied to systems utilizing other gases of relatively low boiling points as refrigerants.

In its preferred form the low temperaturev refrigeration system of the invention comprises:

A compressor;

A heat exchanger; l

An expansion engine comprising a chamber hermetically sealed against the surrounding atmosphere and including a member movable by the expansion of compressed gas in the chamber and force-transmitting means operativelyconnected to the movable member;

A conduit for conveying compressed gas from the compres/ser through the heat exchanger to the chamber of the expansion engine;

A conduit for conveying expanded gas from the chamber to the space to b'e cooled; and

A conduit for conveying the gas from the cooled space to the compressor through the heat exchanger. t

In the accompanying drawings:

Fig. 1 is a diagrammatic representation of a accordance with the principles of the invention, shown, for the purpose of illustration, as applied to the production of liquid oxygen, from air; and

purpose of illustration, to the production of liquid helium.

In the refrigeration system shown in Fig. 1, I0 and II are compression engines which are equipped with suitable means for removing heat of compression, such as coolers Ill and II, and are advantageously either of the floating piston type or the diaphragm type described herein, l2, I3 and I4 are expansion engines of either the floating piston type or the diaphragm type, and I5 and I6 are heat interchangers, preferably of the form described herein. Shown as an illustrative example of the utility of the system is rectifying column I'l for the production of liquid oxygen from air.

Helium is compressed to 30 atmospheres in compressor I0 and air is compressed to 5 atmospheres in compressor II. After cooling, if necessary, to about 25 C. the compressed air and a portion of the compressed helium are passed successively through heat interchangers I5 and I6 in countercurrent heat exchange relation with the cold gaseous nitrogen from the rectifier and with portions of cold expanded helium.

A portion of the helium at 30 atmospheres pressure from compressor I0 is expanded in engine I2 with performance of work toa pressure of 2 atmospheres thereby reducing its temperature to about C. This portion of expanded helium is returned to the, compressor through heat exchanger I5 counter-current to the now of compressed helium and air.

A further portion of the 'compressed helium at approximately 100 C. coming from interchanger I5 is expanded in engine I3 with performance of work to a pressure of 2 atmospheres thereby further reducing its temperature to about C. This second portion of expanded helium is retIurned to compressor I0 through heat interchangers I6 and I5 successively. The remainder of the compressed helium leaving heat interchanger I6 at a temperature of about 175 C. is expanded in engine I4 to 2 atmospheres pressure and a temperature of about 220 C.

In the embodiment of the invention illustrated, this nal low temperature helium is utilized system for the production of low temperatures in 55 for the production of liquid oxygen by passing it through condensing coil I8 in rectifying column Il, wherein it serves to condense nitrogen for re- 3 flux purposes in the column. Air under 5 atmospheres pressure which has passed successively through interchangers I5 and I6 is partially liquefied in the coil at the base of the rectifying column, thereby evaporating liquid oxygen surrounding the coil and providing gaseous oxygen which ascends the column in counterow with descending liquid mixtures. The partially liquefied stream of air is expanded through reducing valve I9 to atmospheric pressure and passed into the middle of the column at approximately the boiling point of liquid air. The expanded helium from coil 8 returns to compressor |0 through heat interchangers i6 and |5 successively. The liquid oxygen fraction collects in the lower portion of the rectifying column. The gaseous nitrogen fraction from the top I the column is returned to the atmosphere through heat interchangers and I6 in counter-current heat is the ratio of the heat capacity for constant pressure to that for constant volume, P1=initial pressure and P2=ilnal pressure, it is evident that with a given quantity of gas expanding from Pi to P2 the amount of refrigeration is proportional to the absolute temperature of the admitted charge of gas.

Since the expansion of compressed gas with the performance of work is an essential feature of the refrigeration system of the invention it is obvious that the successful and efilcient performance of the system depends in very large part upon the engine used for the expansion.

As an example of the utilization of the refrigeration system of the invention, for the production of temperatures below the boiling point of liquid oxygen, Fig. 2 is a diagrammatic representation of a system utilizing the principles of the invention for the production of liquid helium.

In Fig. 2, |50 is the compressor of the refrigerating system, which may be, for example, a

floating piston engine, although conventional compressors may be used. |5| is a conventional cooling device. |52, |53, |54, |55, |56 and |51 are interchangers. |56 and |56 are expansion engines. |60 is an expansion valve. |6| is a reservoir for low pressure helium and |62 is a purifying reservoir.

|63 is a source of gaseous helium to be liquefied, for example, a conventional pressure cylinder and |64 is the liquid helium chamber.

The low temperature elements of the system are surrounded by radiation shield |65. The interior of the chamber formed by the radiation shield |65 or of the walls of the shield is evacuated.

Helium is compressed to 15 atmospheres by compressor |50 and cooled to 30 C. in cooler |5|. A portion, approximately four-lifths, of this 4 helium is cooled to 200 C. in heat interchanger |55, and a portion of this helium at 200 C.

'and l5 atmospheres pressure is expanded in engine, |58 to provide helium at about 225 C., part of which is used to cool helium to be liquefied to about 200 C. in interchanger |52 and part 0f Whih iS utilized to maintain radiation shield |65 at 200 C. or below and to remove a portion of the heat from the compressed helium passing through interchanger |53. l

The remaining portion of the compressed helium at 200 C. from interchanger |53 is cooled to about 253 C. in interchanger |54 and is then expanded in engine |59 to provide helium at about 261 C. for cooling interchanger |56 and interchanger |54 in succession.

A purii'ler |62 is preferablyplaced in this portion of the system at the point of lowest temperature of the compressed helium between interchanger |54 and engine |59. In purifier |62 the helium is caused to pass through a layer of charcoal |61. By placing the charcoal chamber at this point impurities are very eilectively removed from the helium and the helium in the refrigeration system is constantly maintained at a very high degree of purity.

The remaining one-fth of the compressed helium at 30 C. from cooler |5| is passed successively through interchangers |55, |56 and |51 wherein it is cooled successively to 248 C., It is then expanded through valve |60 into the cooling coil |66 of liquefier |64. At this expansion the temperature falls to about 268 C. Liquid helium is produced during the expansion but it evaporates in coil |66 because of the condensation of helium in liquefier |64 at a slightly higher pressure. The cold low pressure helium from coil |66 flows back to compressor |50 through interchangers |51, |56 and |55 in succession. coming from interchanger |52 is further cooled to 261 C. in interchanger |56 before passing to the liquefier.

The expanded gas leaving interchanger |56, instead of being used for the production of liquid helium inside the vacuum chamber, as shown in Fig. 2, may be led outside the chamber to any A point where low temperature refrigeration is desired.

I claim:

1. A low temperature gas cycle refrigeration system comprising a. compressor, a plurality of heat exchangers, a plurality of expansion engines for the expansion oi' compressed gas with the performance of external work each comprising a chamber hermetically sealed against leakage to l and from the surrounding atmosphere and including a member movable by the expansion of compressed gas in the chamber and force transmitting means operatively connected to the movable member, conduit means for conveying a portion of the compressed gas from the compressor through a plurality of said heat exchangers in succession and to one of said expansion engines, conduit means for conveying further portions of said compressed gas from at least one point prior to its passage through the last of said successive heat exchangers to further of said expansion engines, and conduit means for conveying expanded gas from said further expansion engines through said heatexchangers to said compressor counter-current to the flow of said compressed gas, conduit means for conveying said first portion Aof expanded gas to a space to be cooled, and

The helium to be liquefied casacca conduit means for conveying the gas from the cooled space to the compressor through said heat exchangers counter-current and in inverse order to theviiow of said compressed gas.

2. A low temperature gas cycle refrigeration system comprising a compressor, two heat exchangers, three expansion engines for the expansion of compressed gas with the perfomance of external work each comprising a chamber hermetically sealed against leakage -to and from the surrounding atmosphere and including a member movable by the expansion of compressed gas in the chamber and force transmitting means operatively connected to the movable member, conduit means for conveying a portion of the compressed gas from the compressor through said heat exchangers in succession, conduit means for` conveying a further portion of said compressed gas from said compressor to one of said expansion engines, conduit means for conveying the expanded gas from said iirst engine to said compressor through the first heat exchanger counter-current to the flow of the compressed gas therethrough, conduit means for conveying a portion of the compressed gas leaving said first heat exchanger to the second of said expansion engines. conduit means for conveying expanded gas from said second engine through said heat exchangers counter-current and in inverse order to the flow of said compressed gas,`

3. A low temperature gas cycle refrigerationl system comprising a compressor, a heat exchanger, an expansion engine for the expansion of compressed gas with performance of external Work, a second heat exchanger, a second expansio'n engine for the expansion of compressed gas with performance of external work, conduit means for conveying a portion of the compressed gas from the compressor through said first heat exchanger to said iirst expansion engine, conduit means for conveying expanded gas from said first expansion engine through said first heat exchanger counter-current to the iiow of oompressed gas therethrough, conduit means for conveying a further portion of the compressed gas successively through said first and second heat exchangers to said second expansion engine, conduit means for conveying expanded gas from said second expansion engine through a, space to be cooled and thereafter successively through said second and said rst heat'exchangers countercurrent to the flow of compressed gas therethrough.

4. A low temperature gas cycle refrigeration system comprising a compressor, a plurality of heat exchangers, a, plurality of expansion engines for the expansion of compressed gas with the performance of external work, conduit means for conveying a portion of the compressed gas from the compressor through a plurality of said heat exchangers in succession and to one of said expansion engines, conduit means for conveying further portions of said compressed gas from at least one point prior to its passage through the last of said successive heat exchangers to other expansion engines, and conduit means for conveying expanded gas from said other expansion engines through said heat exchangers to said compressor counter-current to the flow of said compressed gas, conduit means for conveying said first portion of expanded gas through a space to be cooled, and conduit means for conveying the gas from the cooled space to the compressor through said heat exchangers counter-current and in inverse order to the ow of said compressed gas.

said expansion engines, conduit means for conveying the expanded gas from said first engine to said compressor through the first of said heat exchangers counter-current to the flow of the compressed gas therethrough, conduit means for conveying a portion of the compressed gas leaving said first of said heat exchangers to the second of said expansion engines, conduit means for conveying expanded gas from said second engine through said heat exchangers counter-current and in inverse order to the ow of said compressed gas, conduit means for conveying the remaining portion of the compressed gas from the second of said heat exchangers to the third of said expansion engines, conduit means for conveying expanded gas from said third expansion engine through a space to be cooled, and conduit means for conveying thev gas from the cooled space to the compressor through said heat exchangers counter-current and in inverse order to the new of said compressed gas.

6. A low temperature gas cycle refrigeration system comprising a iirst heat exchanger, a main conduit for conducting a compressed gas through said first heat exchanger, a, rst expansion engine for expanding compressed gas with the performance of external work, a iirst branch conduit connected with said main conduit after pass'- ing through said iirst heat exchanger for conducting a portion of the compressed gas to said rst expansion engine, a first return conduit connected with said rst expansion engine for conducting expanded gas through said iirst heat exchanger in heat exchange relation to said main conduit, a second expansion engine for expanding compressed gas with the performance of external work, a second heat exchanger, a, second branch conduit connected with said main conduit after passing through said first heat exchanger for conducting another porion of compressed gas through said second heat exchanger and then to said second expansion engine, an exhaust conduit for conducting expanded gas from said second expansion engine to a space to be cooled, and a second return conduit for conducting the expanded gas from said space to be cooled through said second heat exchanger in heat exchange relation to said second lbranch conduit and then through said rst heat exchanger in heat exchange relation to said main conduit.

7. A low temperature gas cycle refrigeration system comprising a heat shield deiining an enclosure, a first heat exchanger and a second heat exchanger within said enclosure, an expansion engine, a duct in heat exchange relation with a space to he cooled within said enclosure, said duct having an inlet provided with an expansion valve and an outlet, said expansion engine being operative to expand compressed gas with the performance of external work, a. main conduit adapted to be connected with a source of compressed gas, said main conduit having a nrst branch and a second branch, said first branch being arranged to conduct a portion of compressed gas from said main conduit through said first heat exchanger and then to said expansion engine, an exhaust conduit for conducting the expanded gas lfrom said expansion engine about said heat shield and then through saidfirst heat exchanger in heat exchange relation to said first branch conduit, said second branch being arranged to conduct another portion of compressed gas from said main conduit through said second heat exchanger and then to said expansion valve, and a return conduit for conducting the expanded gas from the outlet of said duct through said second heat exchanger in heat exchange relation to said second branch.

8. A low temperature gas cycle refrigeration process which comprises dividing a continuous main stream of compressed gas into a first stream and a second stream f compressed gas, expanding said first stream of compressed gas with the performance of external work to produce a first stream of expanded gas, ,passing said first stream of expanded gas into heat exchange relation with said main stream of compressed gas, expanding said second stream of compressed gas with the performance of external work to produce a second stream of expanded gas, and passing said second stream of expanded gas successively into heat exchange relation with a space to be cooled, with said second stream of compressed gas and with said main stream of compressed gas.

9. A low temperature gas cycle refrigeration process which comprises dividing a continuous main stream of compressed gas into a first stream and a second stream of compressed gas, expanding said Afirst stream of compressed gas with the performance of external work to produce a first stream of expanded gas, passing said first stream of expanded gas into heat exchange relation with said second stream of compressed gas and with said main stream of compressed gas, expanding said second stream of compressed gas with the performance of external work to produce a second stream of expanded gas, and passing said second stream of expanded gas successively into heat exchange relation with a space to be cooled,

with said second stream of compressed gas and with said main stream of compressed gas.

10, A low temperature gas cycle refrigeration process which comprises dividing a continuous main stream of compressed gas into a first stream and a second stream of compressed gas, expanding said first stream of compressed gas with the performance of external work to produce a first stream of expanded gas, passing said first stream of expanded gas into heat exchange relation with said second stream of compressed gas, dividing said second stream of com-pressed gas into a third stream and a fourth stream of compressed gas. expanding said third stream of compressed gas with the performance of external work to produce a second stream of expanded gas, passing said second stream of expanded gas successively into heat exchange relation with said fourth stream of compressed gas and with said second stream of compressed gas, expanding said fourth stream of compressed gas to produce ,a third.

exchange relation with a space to be cooled, with said fourth stream of compressed gas an'd with said second stream of compressed gas.

A 11. A low temperature gas cycle refrigeration process which comprises dividing a continuous main stream of compressed gas into a first stream and a second stream of compressed gas, expanding said first stream Aof compressed gas with the performance of external work to produce a first stream of expanded gas, passing' said rst stream ofexpanded gas successively into heat exchange relation with a zone interposed between the ambient atmosphere and a space to be cooled and with said main stream of compressed gas, expanding said second stream of compressed gas to produce a second stream of expandedgas, and passing said second stream of expanded gas successively into heat exchange relation with the space to be cooled, with said second stream of compressed gas and with said main stream of compressed gas.

12. A low temperature gas cycle refrigeration process which comprises dividing a continuous y main stream of compressed gas into a first stream and a second stream of compressed gas, dividing said first stream of compressed gas into a third stream and a fourth stream of compressed gas, expanding said third stream of compressed gas to product a first stream of expanded gas, passing said first stream of expanded gas into heat exchange relation with said first stream of compressed gas, expanding said fourth Stream of compressed gas to produce a second stream of expanded gas, passing said second stream of expanded gas successively into heat exchange relation with said s cond stream of compressed gas, with said fourth stream of compressed gas and with said first stream of compressed gas, ex- -panding sala .second stream of compressed gas to produce a third stream of expanded gas, and passing said third stream of expanded gas successively into heat exchange relation with a space to be cooled and with said second stream of compressed gas.

13. A low temperature gas cycle refrigeration process which comprises dividing a continuous main stream of compressed helium into a first stream and a second stream of compressed helium, expanding said first stream of compressed helium with the performance of external work to .produce a first stream of expanded helium. passing said rst streamer expanded helium into heat exchange relation with said main stream of compressed helium, expanding said second stream of compressed helium to produce a second stream of expanded helium, passing said second stream of expanded helium successively into heat exchange relation with a space to be cooled, with said second stream of compressed helium and with said main stream of compressed helium, and causing said first stream of expanded helium to pass, prior to passing it in heat exchange relation with said main stream of compressed helium, between said second stream of expanded helium and said space to be cooled, on the one hand, and the ambient atmosphere. on the other hand. 4

, v 14. A low temperature gas cycle refrigeration to produce a first stream of expanded helium, passing said first stream of expanded helium into heat exchange relation with said second stream of compressed helium, dividing said second stream of compressed helium into a third stream and a fourth stream of compressed helium. expanding said third stream of compressed helium with the perfomance of external work to produce a second stream of expanded helium, passing said second stream of expanded helium successively into heat exchange relation with said fourth stream of compressed helium and with said second stream of compressed helium, expanding said fourth stream of compressed helium to produce a third stream of expanded helium, and passing said third stream of expanded helium successively into heat exchange relation with a space to be cooled. with said fourth stream of compressed helium and with said second stream of compressed helium.

SAMUEL C. COLLINS.

REFERENCES CITED The following references are of record in the ille of this patent: 

